The Massachusetts Male Aging Study (MMAS) is considered a landmark research effort in the fields of aging, urology, and endocrinology. It employs a random sample of community-dwelling men (not a convenience sample of patient volunteers). Its size permits estimation of even relatively rare phenomena (e.g., hypogonadism). It is longitudinal (intra-subject variation) not cross-sectional (inter-subject variation) and has successfully followed a cohort from 987-89 (T1) through 1995-97 (T2). Worldwide, it remains the largest male endocrine database. It is the first and still the only major longitudinal study of ED. It is multidisciplinary. The MMAS team has been extraordinarily productive. Emphasis has been given to the practical clinical applications of scientific findings. The proposed project ("EPIDEMIOLOGY OF HORMONES AND ERECTILE DYSFUNCTION IN AGING MEN") is designed to extend the highly productive MMAS by following a projected 800 already participating subjects through a third wave (T3). Building directly on earlier work we will: continue investigation of life-span changes in 14 carefully selected hormones in the same subjects; precisely delineate any hypogonadal syndrome and its major correlates; continue pioneering work on erectile dysfunction (ED) and its various predictors; precisely measure the hypothesized relation between ED (sentinel event) and subsequent CVD; extend knowledge concerning ED-related utilization behavior and quality of life in older men; and assess the validity of the single question measure of ED against a clinical urologic examination by a nationally-respected urologist blinded to subjects' self-reported ED status. Methods of data collection will be identical to those used previously for the MMAS. The proposed research will continue to provide the most comprehensive and reliable information available on ED, life-span hormonal changes and their physiological, psychosocial, anthropometric, and behavioral predictors in normally aging men. Prior to the MMAS there was: (a) no well-designed prospective study describing life span changes in endocrine functioning (hormones) in normally aging men; and (b) no definitive population-based study of ED and its biobehavioral correlates.